1. Field
The field of the invention is stylus designs for handheld pneumatic scribers.
2. Prior Art
The prior art of hand-held pneumatic scribing devices is exemplified by the air scribe of FIGS. 1-7. (Prior art), having an outer shell housing 11, also serving as a handle, and a reciprocating piston 12 operated by compressed air provided from a flexible hose 13. The sliding piston is propelled into reciprocating motion by air from hose 13 provided through passages 14. The piston has passages therein, not shown, which are opened or closed according to the piston position to cause the piston to rapidly reciprocate, striking anvil end 15 of stylus assembly 16 repeatedly.
O-rings 17 are utilized between flange 18 of stylus assembly 16 and a shoulder 19 of a stylus holding bushing 20 pressed into the open end of the handle portion of outer housing 11. The O-rings 17, compressed when the stylus assembly 16 is struck by the piston 12, act as a spring to return the stylus assembly toward the withdrawing piston. In the prior art assembly, the stylus holding bushing 20 may also comprise a pair of ball bearings 22 held in place by sleeve 23 rotated to position one of the ball bearings into contact with a rotation restraining flat area provided upon a version of the stylus having a chisel-like end or the like. (FIG. 7, PRIOR ART) In the present inventive stylus/bushing 10, however, the ball bearings are not needed and the bushing 20 is designed accordingly.
The prior art stylus assembly is of very limited longevity. As seen in prior art FIGS. 2a and 3, the stylus assembly has only a short, small diameter, working tip 24 of tungsten carbide, press fitted into a bore 25 in the end of reciprocating stem 26. The stylus tip 24 and the end of the stem typically break away within a very few hours of use and often after only a few minutes. The small, very hard, tip element is typically forcibly hammered repeatedly against the bottom 27 of bore 25, creating such high and concentrated stresses that the tip 28 of stem 26 breaks away because of rapid fatigue failure.
Therefore, there exists a definite need to replace the prior art stylus and accompanying bushing with designs having much longer useful lives.